I would advise against correcting a college professor. It has been my experience that many professors, especially if they hold a Doctorate, have rather large egos that don't tolerate being corrected in public. These professors do have power over their students, and I wouldn't put it past any of them to get a little "payback" when grading assignments.
My advice is to make a mental note of the error, know that you know the truth, and maintain a low profile until you complete the course and escape from the moron's sphere of influence.